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cmd/vet: %w in Printf call should be flagged #35472

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josharian opened this issue Nov 8, 2019 · 9 comments
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cmd/vet: %w in Printf call should be flagged #35472

josharian opened this issue Nov 8, 2019 · 9 comments
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@josharian
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package main

import (
	"errors"
	"fmt"
)

func main() {
	err := errors.New("ABC")
	fmt.Printf("error: %w\n", err)
}

https://play.golang.org/p/-kQ6HtIIMG7

vet should complain about the %w verb. Only in Errorf format strings does it have meaning.
@josharian josharian mentioned this issue Nov 8, 2019
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@bcmills
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bcmills commented Nov 8, 2019

CC @ianthehat @matloob @dominikh

@bcmills bcmills added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Nov 8, 2019
@bcmills bcmills added this to the Backlog milestone Nov 8, 2019
@mvdan mvdan added the Suggested Issues that may be good for new contributors looking for work to do. label Nov 9, 2019
@mvdan
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mvdan commented Nov 9, 2019

This also seems like a pretty simple issue for anyone wanting to get started contributing to vet.

@Inconnu08
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I would love to take a shot on this. Any pointers to get started on this issue?

@agnivade
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The file in question is this one - https://github.com/golang/tools/blob/master/go/analysis/passes/printf/printf.go. Look at how other verbs are handled and take it from there.

@Inconnu08
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Ah I'm on the right track then. Thank you! I'm working on this 😃

@bcmills bcmills removed the Suggested Issues that may be good for new contributors looking for work to do. label Nov 12, 2019
@Inconnu08
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vet already complains about the %w verb in printf. I ran the above code and this is what I got:
./main.go:10:2: Printf format %w has unknown verb w.

@agnivade
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You are right. This was fixed by golang/tools@1d17272. The original issue was reported by @josharian himself which was about passing strings to a %w parameter. But the commit reported usages of %w with non-Errrof functions too.

The error message is Printf call has error-wrapping directive %w though, not the one you mentioned.

I will go ahead and close this one. Thanks for looking into it @Inconnu08.

@Inconnu08
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Exactly. But the end error message is the above one reported by vet. Anytime!

@josharian
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Oops, sorry. :( I thought I tested with tip but apparently only did 1.13. Thanks, @Inconnu08.

invidian added a commit to flexkube/libflexkube that referenced this issue Nov 24, 2019
@invidian
Don't use %w formatting for non-Errorf statements
238aa6a 
Refs golang/go#35472

Signed-off-by: Mateusz Gozdek <mgozdekof@gmail.com>
@loriscn12 loriscn12 mentioned this issue Jul 7, 2020
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@golang golang locked and limited conversation to collaborators Nov 14, 2020
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